1. Field Of The Invention
The present invention relates to an improved process of producing amino alkylene phosphonic acids and more particularly to a process of producing substantially pure, crystalline amino methylene phosphonic acids in a high yield.
2. Description Of The Prior Art
Heretofore amino methylene phosphonic acids have been prepared, for instance, by reacting amines with formaldehyde and a compound of the trivalent phosphorus, such as phosphorus acid, esters of phosphorous acid, or phosphorus trichloride according to the following equation: ##EQU1## However, the yields obtained when proceeding according to this known process, are rather low and usually do not exceed about 55 % to 60 %. These low yields are due to the formation of oily by-products which are formed, for instance, on reacting ethylene diamine, formaldehyde, and phosphorus trichloride and which consist of ethylene diamine tri-(methylene phosphonic acids) and di-(methylene phosphonic acids) and other reaction products, and the separation of which from the resulting ethylene diamino tetra-(methylene phosphonic acid) is quite difficult.